The present invention relates to a method of bending pipes by means of a bending machine having a supporting mandrel attached to a connecting rod. The invention relates also to a mandrel for such a bending machine for carrying out the bending method.
In bending pipes on a bending machine it has been known to use a supporting mandrel attached to a mandrel rod. In general, the conventional supporting mandrels are either rigid mandrels in the form of a spoon-shaped mandrel or a spherical mandrel, or particularly in bending thin walled pipes also the so-called links or articulated mandrels.
In all prior art mandrels of this kind, the interior support of the pipe to be bent takes place only over a relatively minute length section as compared to the overall length of the bend. Moreover, during the bending process there occurs a relative movement between the pipe being bent and the supporting mandrel so that apart from bending forces also frictional forces resulting from the relative movement must be overcome by the bending machine. Another disadvantage is the risk that due to the relative movement the mandrel creates grooves or scorings in the inner wall of the pipe.
In another prior art bending method the pipe is filled up with a loose material such as, for example, sand or with a meltable filling substance such as, for example, synthetic resin or paraffin. The filling material or substance, however, after completion of the bending process has to be withdrawn which processing step is time consuming and expensive. Consequently, the latter method is employed only in the single part production. In the production using a bending machine, the method based on the filling material is impractical.